Magnetic media are widely used in various applications, particularly in the computer industry, and efforts are continually made with the aim of increasing the areal recording density, i.e., bit density of the magnetic media. In this regard, so-called “perpendicular” recording media have been found to be superior to the more conventional “longitudinal” media in achieving very high bit densities. In perpendicular magnetic recording media, residual magnetization is formed in a direction perpendicular to the surface of the magnetic medium, typically a layer of a magnetic material on a suitable substrate. Very high linear recording densities are obtainable by utilizing a “single-pole” magnetic transducer or “head” with such perpendicular magnetic media.
Efficient, high bit density recording utilizing a perpendicular magnetic medium requires interposition of a relatively thick (as compared with the magnetic recording layer), magnetically “soft” underlayer (“SUL”) layer, i.e., a magnetic layer having a relatively low coercivity of about 1 kOe or below, such as of a NiFe alloy (Permalloy), between the non-magnetic substrate, e.g., of glass, aluminum (Al) or an Al-based alloy, and the magnetically “hard” recording layer having relatively high coercivity of several kOe, typically about 3-6 kOe, e.g., of a cobalt-based alloy (e.g., a Co—Cr alloy such as CoCrPtB) having perpendicular anisotropy. The magnetically soft underlayer serves to guide magnetic flux emanating from the head through the hard, perpendicular magnetic recording layer.
A typical conventional perpendicular recording system 10 utilizing a vertically oriented magnetic medium 1 with a relatively thick soft magnetic underlayer, a relatively thin hard magnetic recording layer, and a single-pole head, is illustrated in FIG. 1, wherein reference numerals 2, 2A, 3, 4, and 5, respectively, indicate a non-magnetic substrate, an adhesion layer (optional), a soft magnetic underlayer, at least one non-magnetic interlayer, and at least one perpendicular hard magnetic recording layer. Reference numerals 7 and 8, respectively, indicate the single and auxiliary poles of a single-pole magnetic transducer head 6. The relatively thin interlayer 4 (also referred to as an “intermediate” layer), comprised of one or more layers of non-magnetic materials, serves to (1) prevent magnetic interaction between the soft underlayer 3 and the at least one hard recording layer 5 and (2) promote desired microstructural and magnetic properties of the at least one hard recording layer.
As shown by the arrows in the figure indicating the path of the magnetic flux φ, flux φ is seen as emanating from single pole 7 of single-pole magnetic transducer head 6, entering and passing through the at least one vertically oriented, hard magnetic recording layer 5 in the region below single pole 7, entering and traveling along soft magnetic underlayer 3 for a distance, and then exiting therefrom and passing through the at least one perpendicular hard magnetic recording layer 5 in the region below auxiliary pole 8 of single-pole magnetic transducer head 6. The direction of movement of perpendicular magnetic medium 1 past transducer head 6 is indicated in the figure by the arrow above medium 1.
With continued reference to FIG. 1, vertical lines 9 indicate grain boundaries of polycrystalline layers 4 and 5 of the layer stack constituting medium 1. Since magnetically hard main recording layer 5 is epitaxially formed on interlayer 4, the grains of each polycrystalline layer are of substantially the same width (as measured in a horizontal direction) and in vertical registry (i.e., vertically “correlated” or aligned).
Completing the layer stack is a protective overcoat layer 11, such as of a diamond-like carbon (DLC), formed over hard magnetic layer 5, and a lubricant topcoat layer 12, such as of a perfluoropolyethylene material, formed over the protective overcoat layer.
Substrate 2 is typically disk-shaped and comprised of a non-magnetic metal or alloy, e.g., Al or an Al-based alloy, such as Al—Mg having an Ni—P plating layer on the deposition surface thereof, or substrate 2 is comprised of a suitable glass, ceramic, glass-ceramic, polymeric material, or a composite or laminate of these materials; optional adhesion layer 2A, if present, may comprise an up to about 30 Å thick layer of a material such as Ti or a Ti alloy; soft magnetic underlayer 3 is typically comprised of an about 500 to about 4,000 Å thick layer of a soft magnetic material selected from the group consisting of Ni, NiFe (Permalloy), Co, CoZr, CoZrCr, CoZrNb, CoFeZrNb, CoFe, Fe, FeN, FeSiAl, FeSiAIN, FeCoB, FeCoC, etc.; interlayer 4 typically comprises an up to about 300 Å thick layer or layers of non-magnetic material(s), such as Ru, TiCr, Ru/CoCr37Pt6, RuCr/CoCrPt, etc.; and the at least one hard magnetic layer 5 is typically comprised of an about 100 to about 250 Å thick layer(s) of Co-based alloy(s) including one or more elements selected from the group consisting of Cr, Fe, Ta, Ni, Mo, Pt, V, Nb, Ge, B, and Pd, iron nitrides or oxides, or a (CoX/Pd or Pt)n multilayer magnetic superlattice structure, where n is an integer from about 10 to about 25, each of the alternating, thin layers of Co-based magnetic alloy is from about 2 to about 3.5 Å thick, X is an element selected from the group consisting of Cr, Ta, B, Mo, Pt, W, and Fe, and each of the alternating thin, non-magnetic layers of Pd or Pt is up to about 10 Å thick. Each type of hard magnetic recording layer material has perpendicular anisotropy arising from magneto-crystalline anisotropy (1st type) and/or interfacial anisotropy (2nd type).
Another currently employed way of classifying perpendicular magnetic recording media is on the basis by which the magnetic grains are mutually separated, i.e., segregated, in order to physically de-couple the grains and provide improved media performance characteristics. Thus, magnetic media with Co-based alloy perpendicular magnetic recording layers (e.g., CoCr alloys) are typically classified into two distinct types: (1) a first type, wherein segregation of the grains occurs by diffusion of Cr atoms of the magnetic layer to the grain boundaries of the layer to form Cr-rich grain boundaries, which diffusion process requires heating of the media substrate during formation (deposition) of the magnetic layer; and (2) a second type, wherein segregation of the grains occurs by formation of oxides and/or nitrides at the boundaries between adjacent magnetic grains to form so-called “granular” media, which oxides and/or nitrides may be formed by introducing aminor amount of at least one reactive gas, i.e., oxygen (O2) and/or nitrogen (N2) to the inert gas (e.g., Ar) atmosphere during sputter deposition of the Co alloy-based perpendicular magnetic layer. Generally, substrate heating is not required during such reactive sputtering deposition of the magnetic layer.
Perpendicular magnetic recording media may be fabricated according to a procedure wherein a media substrate with a stack of layers formed thereon, including a just-formed, i.e., topmost, perpendicular magnetic recording layer, is removed from the manufacturing apparatus, e.g., a sputtering apparatus, for exposure to the ambient atmosphere in order to form a surface oxide layer on the magnetic recording layer prior to deposition of a protective overcoat layer thereon, e.g., a carbon (C)-based layer, such as diamond-like carbon (DLC). Typically, the sputtering apparatus constitutes one chamber of an in-line or circularly-configured multi-chamber or similar type apparatus, for use in performing large-scale, automated, continuous manufacture of magnetic recording media. However, removal of the media precursor from the multi-chamber sputtering apparatus for performing the surface oxidation treatment by exposure of the media precursor to the ambient atmosphere prior to the carbon deposition step severely impacts the efficiency and manufacturing throughput of the apparatus. Specifically, additional air locks, loading and unloading means, etc., are required for removing media precursors from a continuous manufacturing apparatus in order to perform the ambient oxidation treatment and then supplying the surface-oxidized media precursors to another manufacturing apparatus (or returning them to the previously utilized multi-chamber apparatus) for subsequent processing, e.g., protective overcoat formation. In addition, the removal of the media precursors from the manufacturing apparatus and the surface oxidation treatment via exposure to the ambient atmosphere disadvantageously incur an excessive increase in the overall media manufacturing interval, cost, and efficiency.
Co-pending, commonly assigned U.S. patent application Ser. No. 10/663,698, filed on Sep. 17, 2003 discloses a method for performing surface oxidation of media precursors in a continuous manner by utilizing a manufacturing apparatus comprising a dedicated oxidation treatment chamber or station positioned between the consecutively arranged chambers or stations for sequential deposition of the magnetic recording layer and the protective overcoat layer. According to the invention disclosed therein, the dedicated oxidation chamber or station is supplied with oxygen gas (admixed with an inert carrier gas) at a sub-atmospheric pressure and at ambient (i.e., room) temperature, such that oxidation of the surface of the magnetic recording layer occurs during the interval in which the media precursor transits the chamber at a transport rate consistent with the transport rate through the other processing chambers or stations of the manufacturing apparatus.
Co-pending, commonly assigned U.S. patent application Ser. No. 10/704,746, filed on Nov. 12. 2003 discloses another method for performing surface oxidation of media precursors in a continuous manner, by utilizing a manufacturing apparatus comprising a dedicated thermally assisted oxidation treatment chamber or station positioned between the consecutively arranged chambers or stations for sequential deposition of the magnetic recording layer and the protective overcoat layer. According to the invention disclosed therein, the dedicated thermally assisted oxidation chamber or station is supplied with oxygen gas and includes heating means for maintaining the media precursors at an elevated temperature during treatment therein, such that oxidation of the surface of the magnetic recording layer is facilitated during the treatment interval in which the media precursor transits the chamber at a transport rate consistent with the transport rate through the other processing chambers or stations of the manufacturing apparatus.
However, it is considered that neither of the above-described methods for performing post-deposition oxidation treatment of media precursors in dedicated oxidation chambers or stations will be universally effective, i.e., capable of achieving sufficient or complete surface oxidation of the magnetic recording layer of the media precursor in the treatment interval during which the precursor transits the oxidation chamber or station, irrespective of the nature or composition of the magnetic recording layer. Specifically, the effect of insufficient or incomplete surface oxidation is expected to be greatest with media precursors comprising magnetic recording layers containing one or more difficult-to-oxidize alloying elements, e.g., noble and/or refractory elements.
In view of the foregoing, there exists a clear need for means and methodology for manufacturing improved, high areal recording density, high performance magnetic recording media, which means and methodology avoid the disadvantages and drawbacks associated with the above-described means and methodology, and which facilitate high throughput, cost-effective, automated manufacture of high performance magnetic recording media, e.g., perpendicular media.
The present invention, therefore, addresses and solves the above-described problems, drawbacks, and disadvantages relating to the inadequate or incomplete surface oxidation associated with the above-described means and methodology for the manufacture of high performance magnetic recording media, particularly perpendicular media, while maintaining full compatibility with all aspects of automated magnetic media manufacture.